U.S. patent number 5,166,376 [Application Number 07/765,969] was granted by the patent office on 1992-11-24 for process for refining vegetable oil.
This patent grant is currently assigned to Mitsubishi Kakoki Kaisha Ltd., Toto Ltd.. Invention is credited to Nobuyuki Maebashi, Hiashi Nogaki, Akiteru Noguchi, Shigemi Suzuki, Akio Tamaki, Shigeru Yamano.
United States Patent |
5,166,376 |
Suzuki , et al. |
November 24, 1992 |
**Please see images for:
( Certificate of Correction ) ** |
Process for refining vegetable oil
Abstract
A process for refining vegetable oil from a miscella obtained by
extraction of vegetable seeds with an organic solvent, which
comprises permeating the miscella through an ultrafilter made of an
inorganic microporous membrane having a pore size of from 30 to 100
.ANG. in a state heated at a temperature of from 50.degree. to
120.degree. C. to remove impurities contained in the miscella.
Inventors: |
Suzuki; Shigemi (Chigasaki,
JP), Maebashi; Nobuyuki (Chigasaki, JP),
Yamano; Shigeru (Chigasaki, JP), Nogaki; Hiashi
(Chigasaki, JP), Tamaki; Akio (Kawasaki,
JP), Noguchi; Akiteru (Kawasaki, JP) |
Assignee: |
Mitsubishi Kakoki Kaisha Ltd.
(Tokyo, JP)
Toto Ltd. (Kitakyushu, JP)
|
Family
ID: |
17260737 |
Appl.
No.: |
07/765,969 |
Filed: |
September 26, 1991 |
Foreign Application Priority Data
|
|
|
|
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Sep 26, 1990 [JP] |
|
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2-254137 |
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Current U.S.
Class: |
554/10; 554/175;
554/12; 554/212 |
Current CPC
Class: |
B01D
61/145 (20130101); B01D 67/0048 (20130101); C11B
3/008 (20130101); B01D 71/02 (20130101); B01D
2325/04 (20130101) |
Current International
Class: |
B01D
71/00 (20060101); C11B 3/00 (20060101); B01D
61/14 (20060101); B01D 71/02 (20060101); C07C
001/00 () |
Field of
Search: |
;260/428
;554/212,175,10,12 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Chemical Abstracts, vol. 106, #6, p. 179, 1987, 35918q..
|
Primary Examiner: Dees; Jose G.
Assistant Examiner: Carr; Deborah D.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt
Claims
What is claimed is:
1. A process for refining vegetable oil from a miscella obtained by
extraction of vegetable seeds with an organic solvent, which
comprises permeating the miscella through an ultrafilter made of an
inorganic microporous membrane having a pore size of from 30 to 100
.ANG. in a state heated at a temperature of from 50.degree. to
120.degree. C. to remove impurities contained in the miscella.
2. The process according to claim 1, wherein the inorganic
microporous membrane is a membrane formed on an inorganic porous
substrate.
3. The process according to claim 1, wherein the vegetable seeds
are soybean, rapeseed, safflower, corn, sunflower or rice bran.
4. The process according to claim 1, wherein the organic solvent is
an aliphatic hydrocarbon, an alicyclic hydrocarbon, an aromatic
hydrocarbon, an aliphatic ketone or an aliphatic ester.
5. The process according to claim 1, wherein the organic solvent is
n-hexane.
6. The process according to claim 1, wherein said temperature is
from 50.degree. to 90.degree. C.
7. The process according to claim 1, wherein the inorganic
microporous membrane is made of zirconium oxide, tin oxide,
titanium oxide or cesium oxide.
8. The process according to claim 1, wherein the inorganic
microporous membrane has a thickness of from 0.2 to 10 .mu.m.
9. The process according to claim 1, wherein the miscella is
permeated through the ultrafilter under a pressure of from 1 to 10
kg/cm.sup.2.
10. The process according to claim 1, wherein the miscella is
circulated at a liquid speed of from 0.5 to 6 m/sec against the
surface of the ultrafilter.
11. The process according to claim 1, wherein the miscella contains
about 25 to 35% by weight of glycerides.
12. The process according to claim 9, wherein the miscella is
permeated through the ultrafilter under a pressure of from 2 to 5
kg/cm.sup.2.
13. The process according to claim 10, wherein the miscella is
circulated at a liquid speed of from 2 to 5 m/sec against the
surface of the ultrafilter.
14. The process according to claim 1, wherein said impurities
removed comprise phospholipids.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for refining vegetable
oil by subjecting a miscella obtained by extraction of vegetable
seeds with an organic solvent to ultrafiltration.
2. Discussion of Background
Conventional vegetable oils used as edible oils include soybean
oil, rapeseed oil, safflower oil, corn oil, sunflower oil and rice
bran oil. To obtain such vegetable oils, it is common to extract a
raw material with an organic solvent such as n-hexane to obtain a
miscella and to remove the organic solvent from this miscella to
obtain a crude glyceride oil. This crude glyceride oil usually
contains from 0.5 to 3% by weight of waxes such as higher alcohols
and impurities such as peptides, organic sulfur compounds,
carbohydrates, fatty acids, hydrocarbons, sterol, lower ketones,
lower aldehydes and coloring matters, in addition to phospholipids
such as lecithin.
It is necessary to remove such impurities from the crude glyceride
oil, since such impurities tend to decompose or polymerize, whereby
oils tend to be colored and bad odors are likely to be generated.
As a conventional process for removing impurities from a crude
glyceride oil, there is, for example, a process as shown in FIG. 3,
wherein firstly, in a process of removing gums, water is added to
the crude glyceride oil to hydrate the gum substance composed
mainly of phospholipids (hydration), followed by centrifugal
separation to remove the gum substance. Even by this hydration,
phospholipids can not completely be removed. Therefore, at the
beginning of the subsequent process of removing acids, phospholic
acid (or citric acid) is introduced to further form a gum
substance, and then an alkali such as caustic soda is added for
saponification of fatty acids, so that the gum substance and fatty
acids form a slime, and the slime is then removed by a centrifugal
separator. Further, water is added for the purpose of e.g. removal
of the added reagents to form a slime, and this slime is removed by
a centrifugal separator. Then, in a bleaching and deodorizing step,
coloring matters and impurities which could not be removed by the
above alkali refining, such as heavy metals, fatty acids, soap
materials, and gum substance, are removed by adsorption and vacuum
distillation to obtain purified vegetable oil. As described in the
foregoing, in the conventional process for removing the gum
substance, slime, etc. from the crude glyceride oil, the
purification process is complicated, the utility costs such as
costs for chemical reagents are substantial, and the vegetable oil
is lost when the gum substance, etc. are discharged from the
centrifugal separator.
In a process proposed to solve such problems, Japanese Unexamined
Patent Publication No. 153010/1975 proposes to use an
ultrafiltration membrane made of polysulfone, polyaclylonitrile or
polyamide and Japanese Unexamined Patent Publication No. 19499/1983
proposes to use a polyimide-type ultrafiltration membrane, and the
proposed process comprises diluting a crude glyceride oil with an
organic solvent such as n-hexane, contacting the diluted oil with
the ultrafiltration membrane under pressure, and removing the
organic solvent from the permeate to obtain purified vegetable
oil.
However, in the process wherein the above-mentioned ultrafiltration
membrane is employed, a non-aqueous organic solvent is contacted
with an organic compoundbased filtration membrane, whereby the
operation temperature is rather limited, and it is required to cool
the miscella obtained from the extraction process. Further, when
used for a long period of time, the membrane tends to undergo
swelling by the influence of the organic solvent in the miscella,
whereby there will be a problem such that the degree of selectivity
of cut off limit tends to deteriorate.
SUMMARY OF THE INVENTION
The present invention has been made in view of such problems in the
conventional process, and it is an object of the present invention
to provide a process for obtaining vegetable oil of high purity
free from inclusion of impurities such as phospholipids, by means
of a filtration membrane excellent in the heat resistance and
solvent resistance, capable of providing a high flux rate and free
from swelling even when used for a long period of time.
Thus, the present invention provides a process for refining
vegetable oil from a miscella obtained by extraction of vegetable
seeds with an organic solvent, which comprises permeating the
miscella through an ultrafilter made of an inorganic microporous
membrane having a pore size of from 30 to 100 .ANG.in a state
heated at a temperature of from 50.degree. to 120.degree. C. to
remove impurities contained in the miscella.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a process flow diagram illustrating the process for
refining vegetable oil of the present invention.
FIG. 2 is a diagrammatical enlarged cross sectional view of a
ultrafiltration membrane used in the present invention.
FIG. 3 is a flow chart for a conventional process for purifying a
crude glyceride oil.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The miscella to be used in the present invention is the one
obtained by extracting vegetable seeds with an organic solvent.
As such vegetable seeds, soybean, rapeseed, safflower, corn,
sunflower or rice bran may be used, as mentioned above. However,
the vegetable seeds are not limited to such specific examples.
The organic solvent useful for extracting the vegetable seeds,
includes, for example, an aliphatic hydrocarbon such as pentane,
n-hexane or octane, an alicyclic hydrocarbon such as cyclopropane,
cyclopentane, cyclohexane or cycloheptane, an aromatic hydrocarbon
such as benzene, toluene or xylene, an aliphatic ketone such as
acetone or methyl ethyl ketone, and an aliphatic ester such as
ethyl acetate or butyl acetate. Preferred is n-hexane.
The miscella obtained by extraction of vegetable seeds with an
organic solvent, usually contains glycerides in an amount of from
25 to 35% by weight. However, the content of glycerides is not
limited to such a concentration range.
It has been found that when the miscella is subjected to filtration
by the ultrafilter of the present invention without separating it
into the organic solvent and glycerides by a distillation operation
as was the case in the conventional processes, the flux rate is
high, and the merit supersedes the demerit of an increase in the
amount of liquid by the solvent.
In the present invention, the temperature of the miscella treated
by the ultrafilter is set usually at a level of from 50.degree. to
120.degree. C., preferably from 50.degree. to 90.degree. C., which
is relatively high as compared with a case where a conventional
nonaqueous organic ultrafiltration membrane is employed.
As will be described hereinafter, the ultrafilter to be used in the
present invention is made of an inorganic material such as zircon
(zirconium oxide), and its heat resistance is not limited as
distinguished from the conventional nonaqueous organic filter. The
viscosity of oils tends to decrease logarithmically with an
increase of the temperature, whereby the flux rate through the
filter increases with an increase of the temperature of the
miscella.
Accordingly, in the present invention, the temperature of the
miscella to be treated is set at a level of from 50.degree. to
120.degree. C. If the temperature is lower than 50.degree. C., the
flux rate tends to be low, such being undesirable. On the other
hand, if it exceeds 120.degree. C., recovered phospholipids in the
retentate tend to undergo property changes, such being
undesirable.
The present invention is characterized in that the miscella thus
adjusted to a prescribed temperature, is treated by means of a
ultrafilter made of an inorganic microporous membrane having a pore
size of from 30 to 100 .ANG..
Here, the ultrafilter to be used in the present invention, may be
prepared by a suitable method such as extrusion forming or press
forming using an inorganic material such as glass or ceramics such
as zirconium oxide (ZnO.sub.2), tin oxide (SnO.sub.2), titanium
oxide (TiO.sub.2) or cesium oxide (CeO.sub.2), to form an inorganic
microporous membrane having a pore size of from 30 to 100
.ANG..
If the pore size is less than 30 .ANG., the flux rate of the
miscella tends to be low. On the other hand, if it exceeds 100
.ANG., the degree of selectivity for the separation of gum
substance tends to be low, such being undesirable.
The shape of the ultrafiltration membrane is optional, and it may
be, for example, tubular or monolithic.
The structure of the inorganic microporous membrane is not limited
to a single layer structure. It may have a composite structure
having an inorganic microporous membrane formed on a porous
substrate having a pore size larger than the pore size of the
inorganic microporous membrane, so long as it has at least one
layer of inorganic microporous membrane having a pore size of from
30 to 100 .ANG..
The inorganic microporous membrane is preferably as thin as
possible in order to improve the flux rate. For this purpose, the
composite structure is suitable. In such a case, the thickness of
the inorganic microporous membrane is preferably from 0.2 to 10
.mu.m, and the inorganic microporous membrane preferably has the
smallest pore size among a plurality of layers and constitutes the
outermost layer for contact with the miscella
Such a composite membrane can readily be formed, for example, by
coating a slurry sol of the above inorganic material in a desired
thickness on a porous substrate made of e.g. inorganic material,
followed by dehydration for gellation, drying and calcination.
Phospholipids contained in the miscella have a molecular weight
approximately equal to the molecular weight of triglyceride, but
they are mutually associated to form polymers. Therefore, when such
miscella is treated by the ultrafilter of the present invention,
impurities such as phospholipids contained in the miscella will not
pass through the ultrafilter, whereas the organic solvent solution
containing glycerides will permeate through the filter as a
permeate fraction.
The pressure during the ultrafiltration varies depending upon the
shape of the ultrafilter, but usually within a range of from 1 to
10 kg/cm.sup.2, preferably from 2 to 5 kg/cm.sup.2.
Further, when the miscella is subjected to ultrafiltration under
the above described conditions, it is preferred to circulate the
miscella in a cross flow fashion against the ultrafilter. In such a
case, the liquid speed of the miscella against the membrane surface
of ultrafilter is usually from 0.5 to 6 m/sec, preferably from 2 to
5 m/sec.
Further, the organic solvent solution containing glycerides having
the gum substance such as phospholipids removed therefrom, will
then be subjected to e.g. distillation to remove the organic
solvent, followed by bleaching and deodorizing in accordance with
the conventional methods. Now, the present invention will be
described in further detail with reference to the drawings.
FIG. 1 is a process flow diagram for recovering vegetable oil
according to the present invention. In FIG. 1, a miscella obtained
in a usual continuous extraction step 10 is once stored in a
miscella tank 20. Then, the miscella is sent via a pump Pl to a
solid material removal filter 30 which is a notch wire filter or a
usual microfiltration filter made of a sintered alloy, whereby
solid material contained in the miscella is removed, and then the
miscella is supplied to a service tank 40. The miscella in the
service tank 40 is pressurized to a level of from 2 to 5
kg/cm.sup.2 by a pressure up pump P2 and then preheated to a
temperature of about 70.degree. C. by a preheater 50, and then it
is supplied to an ultrafilter 60 of the present invention of the
first stage.
Here, in order to attain a linear velocity on the surface of the
ultrafiltration membrane, it is preferred to circulate the
retentate by means of a circulation line.
The permeate fraction having impurities such as phospholipids and
waxes thus removed, will be stored in a recovered miscella tank
70.
On the other hand, the retentate discharged from the first stage
ultrafilter 60, having phospholipids and waxes concentrated, is
pressurized to some extent by a pump P4 and then supplied to a
second stage ultrafilter 60'.
Also in the second stage ultrafilter, it is preferred to circulate
the retentate by means of a circulation line in order to attain a
linear velocity on the membrane surface.
The permeate of miscella having impurities such as phospholipids
removed by the second ultrafilter 60' will be stored in the
recovered miscella tank 70 in the same manner as the permeate
fraction of the first stage. The recovered miscella collected in
the recovered miscella tank 70 is then supplied to a solvent
recovery unit (not shown) whereby the glyceride (oil) fraction is
separated from the organic solvent by a distillation operation, and
then bleached and deodorized by conventional methods to obtain
purified vegetable oil.
On the other hand, the retentate having impurities such as
phospholipids further concentrated by the second stage ultrafilter
60' will be stored in a slime tank 80 and then supplied to a
recovery unit (not shown) for recovering a useful component such as
lecithin.
The process flow diagram of FIG. 1 illustrates a case wherein two
stages of ultrafilters are provided. However, depending upon the
concentration of the miscella and the degree of removal of
phospholipids, the number of stages of the ultrafilters may, of
course, be increased.
Now, the present invention will be described in further detail with
reference to Examples. However, it should be understood that the
present invention is by no means restricted by such specific
Examples.
EXAMPLE 1
Using the ultrafilter of the present invention and the process as
shown in FIG. 1, a soybean miscella was purified.
As the ultrafilter, an asymmetric membrane having a composite
structure as shown in FIG. 2 was used.
In FIG. 2, reference numeral 1 indicates a porous alumina (Al.sub.2
O.sub.3) substrate having a thickness of 0.5 mm and a pore size of
from 3 to 13 .mu.m. On one side of this substrate 1, an
intermediate layer 2 having a thickness of from 30 to 60 .mu.m and
a pore size of from 0.5 to 1.0 .mu.m was formed. On one side of
this intermediate layer 2, an active layer 3 having a thickness of
from 10 to 30 .mu.m and a pore size of from 0.05 to 0.15 .mu.m was
formed. Further on one side of this active layer 3, a zirconia
(ZnO.sub.2) microporous membrane 4 having a thickness of from 0.2
to 10 .mu.m and a pore size of 50 .ANG. was formed.
On the other hand, as the first stage and second stage
ultrafilters, ultrafilters comprising a porous alumina substrate
having a diameter of 30 mm and a length of 50 cm and provided with
seven holes each having an inner diameter of 4 mm and a length of
50 cm extending in the longitudinal direction of the substrate and
a zirconia microporous membrane having a pore size of 50 .ANG.
formed by coating zirconia on the inner surface of each hole and
sintering it, were employed. Using such ultrafilters, a soybean
miscella (glyceride component=25-30% by weight, phospholipids=1-2%
by weight) obtained by extracting soybean with n-hexane was heated
to 65.degree. C. by a preheater and treated by the first stage and
second stage ultrafilters by adjusting the linear velocity of the
respective filters to 2.0 m/sec and the pressure on the raw
solution side to 3 kg/cm.sup.2, whereby the flux rate of the
permeate was 130 l/m.sup.2 .multidot.H, the glyceride concentration
in the permeate was from 20 to 25% by weight, the concentration of
phospholipids was from 20 to 30 ppm, impurities such as
phospholipids in the permeate were extremely small, and the
treating capacity was large.
COMPARATIVE EXAMPLE 1
Using the same apparatus as used in Example 1, the treating
temperature was lowered to 40.degree. C., the glyceride
concentration in the permeate was from about 20 to 25% by weight
and the concentration of phospholipids was from 20 to 30 ppm, which
were satisfactory, but the flux rate of the permeate dropped to 90
l/m.sup.2 .multidot.H and the treating capacity decreased
substantially.
COMPARATIVE EXAMPLE 2
A soybean miscella was treated in the same manner as in Example 1
except that an ultrafilter made of a nonaqueous organic membrane
was used instead of the ultrafilter made of the zirconia
microporous membrane.
However, since the used ultrafilter is made of a nonaqueous organic
membrane, the treatment was conducted at 40.degree. C. i.e. at an
acceptable temperature for operation for a long period of time.
As a result, the glyceride concentration in the permeate was from
about 20 to 25% by weight, the concentration of phospholipids was
from 20 to 30 ppm, and the flux rate of the permeate decreased to
72 l/m.sup.2 .multidot.H.
As described in the foregoing, the present invention provides a
process for refining vegetable oil, whereby vegetable oil of high
quality is obtainable with minimum inclusion of impurities such as
phospholipids, and it is possible to reduce the cost of
installation, since the flux rate is high.
The ultrafilter used in the present invention is made of an
inorganic microporous membrane and thus has heat resistance.
Therefore, the miscella can be treated at a considerably high
temperature, whereby the flux rate will be high, and accordingly,
the filter apparatus can be made compact, and the installation cost
can be saved. Further, since the ultrafilter used in the present
invention is an inorganic membrane, the membrane itself will not
undergo a property change even when contacted with the solvent of
the miscella for a long period of time, and there is no
deterioration in the degree of selectivity of cut off limit.
* * * * *